Thanks for writing in!
This is totally normal. When you run a speed test, it temporarily will saturate your bandwidth to "test the pipe" You're seeing that in MultiPing, which is pretty cool in and of itself.
What results are you seeing in MultiPing when you add the new gateway? Can you trace to anything else with MultiPing? Can you use MultiPing and initiate a trace past your gateway (google is a good one to default to)? If you'd like, feel free to drop some screenshots here and I'll give them a look.